We investigated the effect of L-carnitine in seven patients, four female and three male (mean age 44.4 +/- 6.0 years) with chronic renal failure. Six patients, four female and two male (mean age 49.3 +/- 2.2 years) with chronic renal failure were given a placebo (0.9% sodium chloride) as control. After the basal data were obtained, patients received a single intravenous dose of L-carnitine (1 g) or placebo and two hours later insulin sensitivity was studied by the intravenous insulin tolerance test. No change was observed in biochemical data and K(itt) values in the placebo group. K(itt) increased significantly with carnitine (from 2.99 +/- 0.3 to 3.54 +/- 0.2%/min, p < 0.03) compared to the control group (p < 0.02). This result suggests that L-carnitine may improve the insulin resistance common among uremic patients.